The principal aims of the proposed research are: 1. the development of novel spectroscopic methods for the elucidation of the structure and dynamics of macromolecular assemblies; and 2. the application of these techniques to obtain insight into the function of selected membrane systems. We plan to continue several lines of research that have been fruitful: 1. We are continuing our spectroscopic studies of the gramicidin A transmembrane channel. Specifically, we are carrying out energy transfer and nuclear magnetic resonance studies to determine the location of gramicidin in lipid bilayer membranes. X-ray crystallographic studies of gramicidin A and of a cesium derivative are in progress. Our goal is to solve these structures at atomic resolution. 2. We will carry out nanosecond fluorescence studies of proteins and membranes using synchrotron radiation as a pulsed light source to monitor very rapid conformational changes. 3. We are developing new approaches for labeling biological membranes with fluorescent probes. Enzyme-catalyzed insertion appears very promising in this regard. We are designing probes with microsecond to millisecond excited state lifetimes.